Abstract: The prostatic complex of Didelphis virginiana Kerr has been studied by a variety of cytological and cytochemical means. Segment I was characterized by an apocrine type secretory mechanism. The apical parts of the epithelial cells, which were shed into the glandular lumen, contained vesicles which give positive cytochemical reactions for acid phosphatase, aliesterase, 5′-nucleotidase, and nucleoside diphosphatase. These vesicles also contained material which was reactive with the periodic acid-Schiff test for mucopolysaccharide and Baker's test for phospholipid. Segment II was characterized by the presence of two types of cells in the glandular epithelium. Type A cells contained large rounded secretory granules which gave positive reactions for acid mucopolysaccharides but not for proteins. Type B cells contained large elongate secretory granules which gave positive reactions for proteins but not for polysaccharides. Electronmicrographs indicated these secretory granules to have distinctive morphologies and to contain complex crystalloid material. No cells with characteristics intermediate between those of the A and B types were observed. Segment III of the prostatic complex was characterized by the presence of large amounts of glycogen both in the epithelial cells and within the glandular lumen. These observations indicate a remarkable degree of morphological and biochemical heterogeneity on the part of the prostatic complex of this animal.